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A Bandpass Filter Pulls In The Signals
A builder designs a surface-mount bandpass filter board to stop nearby FM broadcast transmitters from overloading receivers on 2 metres and 70 centimetres. The board also includes a low-noise preamplifier and transmit/receive relays.
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555 Makes a Useful Beat Frequency Oscillator
A build uses a 555 timer chip to make a tunable 455 kHz beat frequency oscillator. Injected into a receiver's IF stage, it lets inexpensive sets demodulate CW and SSB signals.